Filter for tobacco smoke



Sept. 4,1956 H. w. KNUDSON FILTER FOR TOBACCO SMOKE Filed April 24, 1956 Patent {FILTERFORTOBACCO SMOKE I-IaroId'WQKmids n, Nor-Wood, Mass., assignor to'H & V

"-Specialties.Co.,Inc.,East Walpole, Mass., 21 corporaiion ofMassachusetts, and P." Lorillard Company, New -.York,"-N.-Y.,- a=corporation of New Jersey, jointly ncafionn ni 24,1956, SerialNo. 580,241

' 2 ,Claims. 31.131-10) I presented, the resolution of which in an individual'case is never a'true solution. The problem is one. which isof increasing magnitude due to the increasing popularity of cigarette smoking.

Even apparently physically sound individuals mayshow minor'blood' pressure "changesydue to-smokingfbut as to these-individuals; nose and throat irritationisof'the greatest concern.

1 My-invention' enables the removal of any desired-proportion of the tars and nicotine present in tobacco smoke -which account for its irritating properties and potential --tox-icity. Actually-of course, complete removalof these substances is not desirable due to considerations of taste --and flavor. Moreover,-in-the event= all of the tars and nicotine are removed no -smoke is produced, i. -e., the smoker draws into his mouth only colorless'and highly unpalatable combustion gases. It is nevertheless signifimeant as illustrating-the remarkablenatureofmy invention :that I- can in' factachieve almost complete removal of:the 'statedvsubstances, and even :within the: limits imposed. .by practical factors such as :the necessity .for maintaining a zfree*.,draw;and the relatively shortv'leng-th .ofnfilter-type :.cigan and cigarette holders.

iMy, invention, as previously windicated;takes; theg-form of at screening-medium or filtendisposedi in .the'path of the, tobacco smoke. .Thefilter .-is .distinguishedingthat it comprises a substantial proportion of, asbestos; orother small diameter fibershaving a; diameter corresponding ,to

, the diameter of the smoke particles to be removed and .beingof the orderof- O. 1 to 0.6 micron; thesefibers being substantially uniformly distributed .in -a loose,-,-unc om- .zpflcted fashion in car-tier .fibers .of; substantially greater ,diameter, the. latter;,being .present,.in .predominant proportion. While mineral fibers, such,as: asbestos :01; glass ,fib,e rs, of,.the.. specified,diameters have been found-to be .particularlysatisfactory, .fibers of a variety of other materials, such as, ny1on, ..celln1ose acetate, viscose rayon, and=polyestergfiberssuch asOrlon. and Dacron,, are satis- .,'factory provided their diameters are within the specified .range.

As apractical matter itis difiicult and expensive to --obtain--a"supply ofsmalldiameterfibers all-of which have a -diameter within the-'range0.1to"0.6 micron-un- "--mixed with any fibersof somewhat-larger diameter,-=and the objects of the present invention cantbe attained by employing, as the source of small diameter fibers, a

"Thus,- I feed togethentoapicker-lapper two laps, one 'con'iprising the cotton fibers, the other the asbestos'gfibers. lhe;picker-lapper-delivers thelaps to thecylinder-of a a cotton --carding-- machine, theproduct of which is a subparticles, usually-40%50%. such filter 1 comprises about 2%'20% possible.

. 2,761,798 F ateritidj Sept. 31,1956

ffibrous material; in" whichsomeof thefibersjhave diameters outside-of =the'0i1to; 0.6 micron range, sayjnythe range of-"0:1 to' 2:0 microns, provided. a, substantial pro- -portion-of=fibers of-the specified diameter are present.

ln thecase of asbestos, it has beenfound tharfibers of the-specified small diameter exist onlyjn theflformpf veryshort lengths most-of them ofthe order of 0 .0Q4 .to -0.0 12 inch irilerigth; although-a few maybe as much as 0.l2='inch='in length. jASbeStQS whichhas be11 f i110l'n- --pletely opened "may contain sticks or bundles which L appear fibrous and --which are considerably longer than ';in'ch,'-;but" these will'have: diameters greater than" 2.0

I microns. Whileother fibers, particularly syntheticfibers, having the specified; small diameter, :may, exist in" longer lengths, substantiallyjll of -the small diameter "(0 11 .10 0.6-micron) fibers'in the filter; of the present invention have; a length iess than 4inch.

T-he carrier fibers m y, :be conventional ,textileffibers, cotton, rayon, or other cellulosic fibers being preferred,

although wool andnylon fibers as well as fibers-of other synthetic materials may also be employed. These fibers normally have-diameters of the order of cotton fibers,

i. e., 1010-25 :microns. }The length ofthecarrier fibers may vary upwardly -fr om'- inch or 'evenless, although they-are-preferably at least Ar'inch long;and may be as much =as several inches long, although normally, ,,,of

--cour se, their length will be no greater" than the over all dimensions of the filter.

I havefound 'that mostysmokersdo not; consider the fiavor'of the tobacco as objectionally'impaired when from 35 6O% by weight of the tars and-nicotine -are removed from i the tobacco smoke. Accordingly, my in- =-vention is; represented in its preferred embodiment-by a filter-manufactured to specifications which provide for the removal-of-from-35%"60% --by weight of jthe smoke Generally and preferably small diameter fibers (-O.10.6 micron) based on the; total--weight-of all the fibers in the filter.

;-It will, of course,be-understood that the quantity of the tobacco=-smoke-particlesremovedis not-entirely a function ofthe concentration of thesmalldiameter fibers since-the density of 'theifibermixture and the diameter and length of the filtermust also be considered. As to cigarettes, I --customarily-prepare' the filter (combining eter-of-about'0-.8l to"0.83 centimetena length of about to centimeters and anapparent specific gravity 0 (weight-per unit-volume grams per cubic centimeter 5 of'fromfllto'0-.23.

*Ihe density-of'the filter is :obviously a most important factorsince there' canbe-no substantial interferencewith draw. It is this limitation on density or compactness particularly which has=prevented the development }of a really satisfactory tobacco smoke-filter heretofore. In-

terestingly, conventional crepe-'paperfilters and filters-of the type compri'sing spunviscose arecapable at'best of removing not more than"5%'30% of the partieles makmg up tobacco -smoke before tmreasonableinterference with draw.

- In the manufacture of =my'filter, it is 'important that 'theblen'dingof' the :two classes of fibers be as uniform as Usingasbestosfibers as the small-diameter fibers and cotton fibers as the carrier fibers, I-custpmarily 'efiect' the blendingon conventional textile machinery.

stantially uniform web of the mixed'fibers-havinga predetermined thickness. -Alternatively, 4 a-mixing picker such as is used in the wool industry may be employed in apparent specific gravity.

chanical strength may be imparted to the roving, when f fibrous material and may replace part the small diameter or the carrier fibers. When a thermoplastic or thermosensitive binder is employed, either in the form of fibers or otherwise, a subsequent heating step f the preliminary blending and the blend may be delivered to the hopper of a wool carding machine. In any case,

' the working in the carding machine not only brings about the'desired blending but also operates to open up the asbestos fibers as is manifestly-necessary. A rod-shaped roving is formed from the web and cut into lengths as determmed by the length of the particular filter. Where encasement of the roving is necessary or considered desirable, the roving may be drawn through a tubular memindicated, by braiding the same with cotton thread or the like, or by applying a hinder or bonding material to the fibrous mixture to bind together the individual fibers or a substantial proportion of them at their intersections to render the filter firm and resilient while retaining its loose uncompacted nature without impairment of draw. Thermoplastic or theirnosensitive materials such as synthetic resinous binders preferably having a softening or activation point of 150300 F. may be applied to the fiber mixture in the form of dry solid particles or liquid droplets or a solution or dispersion'in a liquid medium. If desired, the binder material may itself take the form of a or all of either is required to activate it and bond the fibers together at their. intersections to stabilize the fibrous mass in its loose uncompacted form having the required apparent density. When the binder material is applied to the fiber mixture, care should be exercised to avoid coating the small diameter fibers so asto increase their diameters above the specified size. The proportion of binder material to the total fiber mixture is usually about l%-25% by weight,

, preferably about by weight.

Itis to be clearly understood that the previously stated range on small diameter fiberconcentration is not critical, for I may include either a substantially higher or a substantially lower proportion of such fibers. Even with amounts as low as 1%, I can effect a distinct improvement over crepe paper or all-cotton filters for example. How- ,ever, for best results the content of small diameter fibers .(0.l0.6 micron) should not be much less than about 2% by Weight of the total fiber mixture, preferably at least 5%. Depending upon the demand, the concentration of small diameter fibers in some cases may be as high as or higher than despite the fact that at this point there is definite impairment of tobacco taste and flavor. In the case of filter masses including from 5% to 30% by weight of small diameter fibers there will be present from 70% to 95% by weight of carrier fibers having a diameter on the order of-cotton fibers. Such a filter mass preferably has substantially no greaterresistance to draw than an equal volume of the cigarette tobacco.

The importance of using small diameter fibers of the diameter indicated cannot be overly emphasized. Fibers of greater diameter are relatively ineffective, while smaller diameter fibers have the disadvantage of contributing disproportionately to the air resistance and so are practically inoperable.

Tobacco smoke, as well understood, represents a dispersion of solidand liquid particles in air, the dispersion Y being extremely stable by reason of the small size of the particles, which makes the eifect of gravity negligible compared with the efiect of convection currents and Brownian movement. The manner in which my invention works is perhaps best explained with the aid of diagrams. It has been determined that the diameter of the particles constituting tobacco smoke is about 0.1-0.6 micron. Since the diameter of paper fibers of the type heretofore employed in tobacco filters is of the order of 10-25 microns, there is presented a situation such as portrayed in Fig. l, where A is a smoke particle, B is a cross-section of the paper fiber, C is a slip line representing the flow of the air stream, and D is a similar slip line with the Brownian movement of the particle (denoted by the wavy line F) superimposed thereon. It is clear that if the smoke particle is to be removed from the air stream, it must impinge or collide with the fiber. In the situation represented, the possibility of collisions are obviously remote. One solution to the problem would be to accelerate the particle to such an extent that it would be thrown from the air stream due to its greater inertia into a straight line path E toward the surface of the fiber. However, such a high linear speed manifestly could never be realized under the conditions involved in the problem to which the invention. herein is addressed.

Another angle of attack would be to increase the number of fibers in the path of the particle by closer packing of the fibers and to pass the particle through this tight maze so slowly that it would be bound to collide with one of the fibers due to a diffusion effect. Obviously, this approach is also out of the question because of the limiting conditions here involved.

The invention will be described with reference to. certain embodiments shown in the appended drawings in which:

Fig. 1 is a schematic representation of the path of a smoke particle past a fiber of large diameter;

Fig. 1a is a similar representation of a path of a smoke particle past a fiber of small diameter;

Fig. 2 is an elevation, partly broken away and in section, showing the filter of the present invention embodied in a cigarette;

Fig- 3 is an my invention;

Fig. 4 is a view in elevation, partly broken away and in section, of a smoking pipe embodying the present invention; and

Fig. 5 is a view in elevation, partly broken away and in section, of a cigarette holder embodying the present invention.

Fig. 1a is representative of the mechanism of the filtration as efiected according to the invention. Here, A is the smoke particle, B is a cross-section of a small diameter fiber, preferably an asbestos fiber, having a diameter approaching that of the smoke particle, and C and D are slip lines as in Fig. l, wavy line F denoting the Brownian movement of the particle as in that figure. In this instance, the displacement of the slip lines around the fiber is very slight indeed, and, as a consequence, the particle is almost certain to collide with the fiber and be removed from the air stream-especially when'one considers the deviation resulting from the Brownian movement.

Moreover, it should be pointed out that the particle in Fig. in would not need to be accelerated to nearly as high a linear speed as the particle in Fig. 1 before the inertia of the particle would cause it to deviate sufficiently from the path represented by the slip lines to bring about its collision with the fiber.

The carrier fibers combined in my filter serve to maintain the structure sufiiciently open to allow for easy passage ofair. In the absence thereof, the density of the filter would be such that it would be virtually impossible to draw any smoke through it. As most preferablymanufactured, the resistance of the filter is substantially no. greater than the volume of tobacco as contained in a cigar, cigarette or pipe. Even under these end elevation of another embodiment of conditions, upwards of 35%50% of the tars and nicotin are effectively removed. 1

Forms which my invention may take are illustrated in Figs. 2 to 5, in which the filter material is indicated by the numerals 10, 10 and 1 3" respectively, and may be assumed as combining cotton fibers or other fibers as the carrier fibers and Bolivian blue asbestos as the small diameter fiber component, such asbestos being particularly preferred for use according to the invention. In Fig. 2 the material is shown encased within a cigarette tip 12 which may simulate ivory or cork, for example, the tip having a. slightly greater diameter (exaggerated in the drawing) than the body 14 of the cigarette and being secured thereto by means of a suitable adhesive. In this embodiment the fibrous mass 10 is in the form of a roving having the carrier fibers generally oriented in the direction of travel of the tobacco smoke. Fig. 3 affords an enlarged tip-end view of a cigarette construction in which the filter material in the form of a loose fibrous web 10' is distributed in the folds of a conventional crepe paper filter 16, relatively loosely formed. As shown in Fig. 3,

the crimps of the crepe paper extend generally in the direction of travel of the tobacco smoke. This increases the efiiciency of such a paper filter not less than 500%, assuming a weight ratio as between the fibrous filter material (comprising 2%20% small diameter fibers) and the crepe paper of approximately 1:2.

The filter construction in the pipe represented by Fig. 4 is shown as including a paper casing 18. A cloth casing, for example either finely woven or open mesh, may be substituted.

The filter disposed in the cigarette holder of Fig. 5 is also shown as including a casing of paper or equivalent material. Because of the greater efficiency of the filter, it becomes loaded with tars and nicotone much sooner than conventional filters and accordingly should be changed more often. But the filter, even after the smoking of say ten cigarettes is still upwards of 200% 6 more efiicient than a conventional filter freshly inserted in the holder.

This application is a conticiuation in part of my parent application Serial No. 260,187 filed December 6, 1951, now abandoned, and of my copending application Serial No. 384,673 filed October 7, 1953.

Although I have herein described specific embodiments of my invention, I do not intend to limit myself solely thereto, but to include all of the obvious variations and modifications Within the spirit and scope of the appended claims.

I claim:

1. A tobacco smoke filter comprising a loose mass of intermingled fibrous material having an apparent density from 0.1 to 0.23 gram per cubic centimeter, said mass including a predominant proportion of carrier fibers and a lesser proportion of small diameter fibers, said carrier fibers having a diameter on the order of cotton fibers and said small diameter fibers having a diameter corresponding to the diameter of the smoke particles to be removed and being of the order of 0.1 to 0.6 micron.

2. A cigarette having a filter member for removing a substantial amount of the tars and nicotine from the smoke from said cigarette, said filter member comprising a loose mass of intermingled fibrous material having an apparent density from 0.1 to 0.23 gram per cubic centimeter and having substantially no greater resistance to draw than an equal volume of the cigarette tobacco, and said mass including from to by weight of carrier fibers having a diameter on the order of cotton fibers and from 5% to 30% by weight of small diameter fibers having a diameter corresponding to the diameter or" the smoke particles to be removed and being of the order of 0.1 to 0.6 micron.

No references cited. 

1. A TOBACCO SMOKE FILTER COMPRISING A LOOSE MASS OF INTERMINGLED FIBROUS MATERIAL HAVING AN APPARENT DENSITY FROM 0.1 TO 0.23 GRAM PER CUBIC CENTIMETER, SAID MASS INCLUDING A PREDOMINANT PROPORTION OF CARRIER FIBERS AND A LESSER PROPORTION OF SMALL DIAMETER FIBERS, SAID CARRIER FIBERS HAVING A DIAMETER ON THE ORDER OF COTTON FIBERS AND SAID SMALL DIAMETER FIBERS HAVING A DIAMETER CORRESPONDING TO THE DIAMETER OF THE SMOKE PARTICLES TO BE REMOVED AND BEING OF THE ORDER OF 0.1 TO 0.6 MICRON. 